1. Field of the Invention
The present invention pertains to gravity driven pumps for microfluidic applications, and to microfluidic devices employing such pumps.
2. Background Art
Microfluidic devices are steadily supplanting their macroscale counterparts in numerous applications, particularly in biological and pharmaceutical research. Such devices often require one or more pumps to propel fluid through microchannels. Current methods may employ mechanical pumps such as syringe-type pumps and micromechanical pumps, and non-mechanical pumps such as electrohydrodynamic pumps, electro-osmotic flow pumps, electrowetting pumps, and thermocapillary pumps.
All these pumping systems have drawbacks associated with them. For example, a steady flow rate is difficult to achieve. Moreover, mechanical pumps require an electrical power source, as do pumps which operate based on electrical properties. Most of these pumps are costly and inconvenient to integrate with other microscale devices, and often have slow response times. Electro-osmotic flow pumps have a flow profile which is pH dependent, and which produce stable flow only over a limited pH range. Recently, a thermocapillary pump has been developed. However, this pump requires complex electronic control circuitry and creates heat transfer issues.
The use of gravity-driven flow in microfluidic applications has been attempted. However, conventional reservoirs produce a decrease in hydrostatic pressure as the liquid level in the reservoir drops. This decreasing pressure difference leads to decreased flow rates with respect to time.
It would be desirable to provide a microfluidic system including a microfluidic pump which is simple, economical to produce, and preferably disposable, which can provide a relatively constant and optionally adjustable flow rate, without the necessity for an external power source.